In previous arrangements for conventional reaction type turbines liquid is introduced into the turbine through a distributor. The distributor interconnects the turbine with a volute shaped scroll casing. The distributor includes an internal stay ring comprising an annular array of guide vanes for the purposes of maintaining the sectional shape and integrity of the scroll, and to direct the passage of liquid in relation to a slot-like opening of the distributor to which the scroll casing is connected.
The distributor provides a flow mouth connecting the scroll with the runner of the turbine. The runner of the turbine, for example, may comprise an axial type runner or a Francis type runner. Extending across the slot-like opening of the distributor at the flow mouth are a plurality of wicket gates. The wicket gates are movable between a closed position preventing the flow of such liquid through the flow mouth and an open position permitting liquid flow from the scroll, through the flow mouth of the distributor and across the turbine runner.
Previous designs for the wicket gates have provided a wicket gate having an outer, upstream or leading edge portion and an inner, downstream or trailing edge portion. The outer edge portions of the wicket gates, when in the open position, project forward and displaced from portions of the stay ring. This creates gaps between the wicket gates and the stay ring which are known to trap fish passing through the turbine. Further, the downstream inner edge portion of each wicket gate typically extends over the distributor and, as a result, creates shear forces downstream of the distributor. These shear forces have an adverse effect on any fish swimming through the turbine and passing in the vicinity of these shear forces.
With the increased awareness of the negative impact of the wicket gate structures of previous hydraulic turbines, it is recognized that there is a need for improved structures which are more friendly to fish passing through the distributor.